It is known in the art that plants generally grow well between pH 4 and 7, when supplied with appropriate amounts of water, nutrients, photoradiation, carbon dioxide, and oxygen. Plants don't grow well outside this pH range because of reduced nutrient availability at high and low pH. Every plant variety has an optimal pH, many of which are known in the art.
Hydroponics, the cultivation of plants without soil, provides healthier, disease-free plants, faster than growing in soil. In soil-less culture, plants are instead cultivated using a liquid solution of water and nutrients. The recommended pH for hydroponic culture is usually between 5.5 to 5.8 because overall availability of nutrients is optimized at a slightly acid pH. The availabilities of manganese (Mn), copper (Cu), zinc (Zn) and especially iron (Fe) are reduced at higher pH, and there is a small decrease in availability of phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) at lower pH.
The quality of water used for hydroponics varies widely, because water supplies vary widely. Municipal water supplies vary from each other, and each supply typically varies throughout the year as municipalities change utilization of water sources and as stored water evaporates in dry seasons. In the United States, delivered municipal water is required to be kept above pH 7 to prevent leaching of lead from old plumbing, as occurs when lead contacts acid. Many municipal water supplies are high in alkalinity. Alkalinity is a liquid's ability, or inability, to neutralize acids or hydrogen ions. Most alkalinity in water comes from calcium carbonate (CaCO3) that comes from rocks and soil. Both carbonates and bicarbonates contribute to alkalinity. Water alkalinity is typically measured by the amount of carbonates in the water as parts per million (ppm). Highly alkaline water is more able to neutralize acids. Therefore, high alkalinity water that is above pH 7 requires the addition of more acid to reduce the pH to levels acceptable for hydroponics than low alkalinity water. Of the largest 50 cities in the U.S., about 50% deliver water having alkalinity of over 100 ppm and/or having a pH equal to or higher than pH 8 for at least part of the year. Over 15% of the cities deliver water with a pH equal to or higher than pH 9 and/or with an alkalinity over 200 ppm.
All municipal water supplies in the U.S. would be expected to require addition of acid (to lower pH) before use in a hydroponics system. Many hydroponics nutrient formulas include acids, therefore some municipal water supplies with nutrients require addition of base (to raise pH). The pH of hydroponics systems also changes with time as plants grow and nutrients are used. When water is added to a hydroponics system, if that water contains carbonates, typically the pH is raised and needs to be readjusted. The pH can be measured by a variety of methods known in the art including using pH paper or a pH meter. Typically, the pH of the nutrient solution in a hydroponics system is measured and the pH adjusted before growing begins. Then throughout the growing cycle, the pH is repeatedly measured and adjusted, particularly after adding nutrients or water.
In production hydroponics systems, pH is typically controlled with an automated pH control system that adds acid or base to the nutrient solution. These systems require 3 components: a pH electrode, a pH controller, and a solenoid.
pH buffers are chemicals that when in solution, are resistant to changes in pH. Typically buffers are a combination of a weak acid and its salt or a weak base and its salt. Each chemical buffer has an optimal pH range, where the buffer is most resistant to changes in pH. The optimal pH range is characterized by selected concentrations of the acid or base and its salt. The carbonates causing alkalinity function as buffers and keep the pH high.
pH buffers are used in agriculture and aquaculture for a variety of purposes. AgXplore (Cape Girardeau, Mo., USA) sells a product called Linke, a buffering agent and a compatibility agent that is said to improve the stability of liquid fertilizers when mixed with pesticides and/or micronutrients. Also, many products on the market help stabilize the pH of water in fish aquariums and for building carbonate hardness, typically by using carbonate based buffers. U.S. Pat. No. 5,451,242 and WO 94/08896 describe an active synthetic soil that optionally includes a pH buffer, such as humic acid. The pH of the soil is described to be in a range of pH 5 to pH 7, when the buffer is used from 0 to about 10 parts per 100 parts of zeolite soil mixture.
pH buffers have been described as useful in hydroponics. 95/26130 describes a hydroponic method including a step of adding a pH buffer to the solution. B. Bugbee and F. Salisbury (1985, An evaluation of MES and Amberlite IRC-50 as pH buffers for Nutrient Solution Studies. J. Plant Nutr. 8:567-583) describe use of 2-[N-morpholino]ethanesulfonic acid (MES) at concentrations of 1 and 10 mM as pH buffers for nutrient solution studies for hydroponics. Stabilization of pH in solid-matrix hydroponic systems (HortScience. 1993 28(10):981-4) describes the use of 5 mM and 10 mM MES to stabilize substrate pH of passive-wicking, solid-matrix hydroponic systems. Bruce Bugbee (Nutrient Management in Recirculating Hydroponic Culture, presented at the South Pacific Soil-less Culture Conference, Feb. 11, 2003 in Palmerston North, New Zealand), describes that phosphorous in solution buffers pH, but if phosphorous is maintained at levels that are adequate to stabilize pH (1 to 10 mM), it becomes toxic to plants.
General Hydroponics sells Flora series nutrient products that are said to contain a pH buffer, but the instructions say that adjustment may be necessary since water quality and pH vary both regionally and seasonally.
No products are known to have been described or exist on the market that contain pH buffers and plant nutrients that are useful for stabilizing the pH of a wide range of water supplies without the requirement of additional pH measuring and/or adjustment steps whereby the solution is useful for growing a wide range of plants in a hydroponic system.